amino acids and phospholipids

what is the structure of an amino acid

• amine group

• carboxyl group

• r group

what type of bonds do amino acids form?

peptide bond, condensation reaction, the reaction takes place in the ribosome

what enzyme catalyses the reaction of amino acids?

protease enzyme

what is primary structure?

the specific order of amino acids in a polypeptide

• determined by the DNA sequence of the gene which codes for that polypeptide

what is the secondary structure?

the shape of the chain caused by hydrogen bonds e.g alpha helix or the beta pleated sheet

what is the tertiary structure?

further folding of the secondary structure - active site

what is the quaternary structure?

how individual polypeptide subunits (chains) are arranged with each other to form a larger 3D molecule e.g haemoglobin

what is a prosthetic group?

non-protein molecules forming part of the structure

• proteins with a prosthetic group are called conjugated proteins

what are non polar amino acids?

non polar amino acids have uncharged R groups. they are not attracted to water and are called hydrophobic

what are disulfide bonds?

the covalent bonds between two sulfur molecules, these are relatively strong

what are globular proteins?

• globular proteins tend to have a spherical shape

• they are soluble in water → they have hydrophilic amino acids on their surface

• some roles include enzymes, hormones and oxygen carrying proteins

what are fibrous proteins?

• often play a structural role e.g bones or tendons

• form long rope like molecules

• large proportion of amino acids with hydrophobic R groups → insoluble in water

what is the structure of haemoglobin?

• globular protein with 4 polypeptide subunits

• two are called alpha and two are called beta subunits

• each subunit contains the prosthetic group haem which is an Fe2+ (conjugated protein)

• this is where the oxygen binds, so one haemoglobin molecule can bind to four oxygen molecules

• when one molecule of oxygen joins the quaternary structure changes slightly which makes it more easier for more oxygen to attach

what is the structure of collagen?

• found in skin, tendons and ligaments

• polypeptide chains wrap tightly together to form a triple helix

• every third amino acid is glycine - the R group of glycine is hydrogen - the smallest R group of any amino acid

• the polypeptides can wrap very tightly around each other

• hydrogen bonds form between the polypeptide chains

• polypeptides also joined by strong crosslinks

• large number of polypeptide helixes join together to form microfibrils and fibrils

• the molecules are staggered so there are no weak spots

what is the structure of keratin?

• found in hair and fingernails

• insoluble in water

• consists of long stranded molecules

• high proportion of the amino acid cysteine

• cysteine is used to form disulfide bonds

what is the structure of elastin?

• long strands containing hydrophobic regions

• found in skin and arteries

describe the structure of a phospholipid

• glycerol bonded to two fatty acids and a phosphate

• the phosphate head is negatively charged and is polar (hydrophilic)

• the tails are non polar and hydrophobic

• the tails are joined to the phospholipid via ester bonds

• the phosphate is joined via phosphoester bonds

describe the structure of cholesterol

• hydrophilic hydroxyl group

• rest is hydrophobic

what is the role of cholesterol?

• controls membrane fluidity

• contributes to stability